NSFDEB-NERC: The eco-evolutionary dynamics of age-specific resistance to infectious disease

当疾病流行席卷植物、动物或人类种群时，种群中最年轻的个体往往受到最严重的打击。这是因为青少年通常比成年人更容易感染传染病。事实上，麻疹和水痘等许多人类疾病的传播在很大程度上是由儿童推动的。同样，在许多野生动物物种中，新生的高度敏感的幼虫的春季“脉搏”可能会引发流行病，包括有可能蔓延到人类或牲畜种群的疾病。然而，尽管青少年易受疾病控制的重要性早已被认识到，但我们缺乏对为什么青少年天生如此敏感的基本理解，即使在考虑到以前接触过疾病之后也是如此。这项研究将使用数学模型和模型植物系统的实验来研究驱动特定年龄易感性进化的基本生态和进化过程。这些结果将大大增加我们对抗性进化和疾病传播之间反馈关系的理解，这将改进野生动物疾病的管理策略，并为作物抗病育种提供信息。这项研究还将通过与基础研究相结合的新的公民科学推广活动，增加公众对科学的了解，并丰富当地的生物多样性记录和博物馆藏品。从进化的角度来看，幼虫为什么如此容易受到感染的问题令人费解，因为繁殖前的感染似乎比生命后期(在宿主有机会繁殖之后)感染对宿主的负面影响要大得多。因此，自然选择应该有利于那些年轻时不太容易感染疾病的人。该项目将检验这一新的假设，即幼虫的易感性是通过寄主抗性的进化变化和疾病丰度的生态变化之间的反馈来维持的。这些“生态进化”反馈之所以发生，是因为宿主种群中任何年龄的抗病能力的进化反过来可以降低疾病流行的强度。关键的是，较低的疾病水平使宿主不太可能在青少年时期遭遇疾病，从而使青少年保持易感性。研究人员将在这一新颖的生态进化框架的基础上，开发一种预测性数学理论，以了解关键的宿主和病原体特征，以及驱动特定年龄疾病易感性进化的反馈。然后，为了确定这些特定年龄的选择压力是如何在现实系统中实例化的，并测试来自模型的关键预测，研究团队将利用模型植物-病害系统--白露地(Silene Atifolia)上的花药黑穗病(Microbotryum)，来量化在一系列疾病频率下特定年龄的抗性的适应成本、收益和进化潜力。为了增加拟议工作的更广泛的影响和社会效益，他们将邀请当地自然历史学会参与关于“微型真菌”的分布和多样性的原创性科学研究，并为本科生提供有意义的研究机会。

When a disease epidemic sweeps through a population of plants, animals, or humans, the youngest individuals in the population are often hardest hit. This is because juveniles are typically more susceptible to infectious disease than adults. Indeed, the spread of many human diseases such as measles and chicken pox is largely driven by children. Likewise in many wildlife species, the spring 'pulse' of new highly susceptible young can drive epidemics, including diseases that risk spilling over into human or livestock populations. However, while the importance of juvenile susceptible to disease control has long been recognised, we lack a basic understanding of why juveniles are inherently so susceptible, even after accounting for prior exposure to disease. This research will use mathematical models and experiments with a model plant system to investigate the fundamental ecological and evolutionary processes driving the evolution of age-specific susceptibility. The results will substantially increase our understanding of the feedbacks between resistance evolution and disease spread, which will improve management strategies for wildlife disease, and inform crop breeding for disease resistance. The research will also increase public understanding of science and enrich local biodiversity records and museum collections through new citizen science outreach activities that are integrated with the basic research. The question of why juveniles are so susceptible is puzzling from an evolutionary perspective because infection prior to reproduction would seem to have a much greater negative impact on a host than infection later in life (after the host has had a chance to reproduce). Natural selection should therefore favour individuals that are less susceptible to disease when they are young. This project will test the novel hypothesis that juvenile susceptibility is maintained by feedbacks between evolutionary change in host resistance and ecological change in disease abundance. These "eco-evolutionary" feedbacks occur because the evolution of disease resistance at any age in the host population can in turn reduce the intensity of disease epidemics. Critically, lower disease-levels make it less likely that a host will encounter disease as a juvenile, thereby allowing the maintenance of juvenile susceptibility. The researchers will build on this novel eco-evolutionary framework to develop a predictive mathematical theory for understanding key host and pathogen traits, and the feedbacks driving the evolution of age-specific disease susceptibility. Then to establish how these age-specific selection pressures are instantiated in a real-world system and to test key predictions from the model, the research team will utilise the model plant-disease system, anther-smut disease (Microbotryum) on white campion (Silene latifolia) to quantify the fitness costs, benefits, and evolutionary potential of age-specific resistance under a range of disease frequencies. To increase the broader impacts and societal benefits of the proposed work they will engage local natural history societies in original scientific research on the distribution and diversity of 'micro-fungi', and provide meaningful research opportunities for undergraduates.